During the epizootic of highly pathogenic avian influenza subtype H5N8 in Serbia in the winter of 2016-2017, the highest percent of mortality due to this infection was recorded in mute swans (Cygnus olor). Besides mute swans, avian influenza virus subtype H5N8 was also diagnosed in a small number of hens in rural households. Pancreatic tissues from avian influenza H5N8 positive mute swans and hens that died during this outbreak were collected to determine the character of morphological lesions and the distribution of the viral antigen in this organ. Macroscopic examination of the pancreas of mute swans revealed hemorrhages as well as necrosis, while there were no macroscopic visible lesions in the pancreas of infected hens. Despite the different macroscopic finding, microscopic examination of the pancreas of both infected bird species revealed lesions in the form of acute pancreatitis and multifocal acinar necrosis. The viral antigen was abundantly expressed in the cytoplasm and nucleus of necrotic cells, as well as in macrophages in both examined bird species. Immunohistochemical expression of the viral antigen in the pancreas was strongly consistent with histological lesions. According to the above described findings, it could be concluded that highly pathogenic avian influenza virus H5N8 has a high affinity to pancreatic tissue in both mute swans and hens and the distribution and the character of the lesions in the pancreas are similar in both bird species.
